With the increasing awareness of preventing environmental pollution, there have also been increasing efforts directed to the problems of cleaning up contamination left at abandoned or retired processing facilities. In particular, much effort has been directed to the cleanup of soil contaminated with organic matter, such as oil and tar. There are many sites worldwide where the soil has been contaminated with oil, tar and other hydrocarbon residues. A variety of coal/petroleum-based industrial sites have soil contaminated by spills that may occur during oil production or transportation, or from tailing ponds produced during heavy oil production. These sites include former manufactured gas plant (MGP) sites, where tar and oil from gas production were often disposed of near the production facilities.
One method used in the cleanup of soil contaminated with petroleum by-products and MGP residual wastes is the disposal of such contaminated soils by incineration at a power plant. This method is simple, relatively inexpensive and effective as a treatment for disposing of the contaminated soil. However, this method of treatment is no longer allowed under the Resource Conservation and Recovery Act (RCRA), if the contaminated soil is considered hazardous.
The Environmental Protection Agency (EPA) considers a material to be hazardous when certain chemicals can be leached out in concentrations above predetermined thresholds. EPA employs a leaching test known as the Toxicity Characteristic Leaching Profile (TCLP) test to determine whether a material should be classified as hazardous. Contaminated soils from MGP sites will often be classified as hazardous, as determined by the TCLP test, because chemicals, such as benzene, toluene, ethyl benzene, xylene, among others (also known in the industry as "BTEX"), will leach from the soil.
For instance, soil which produces a leachate of 500 ppb. of benzene in the TCLP test is currently considered to be hazardous. Beyond the current EPA requirements, leachability of compounds is a common regulatory criteria for judging contaminated soils. Environmental standards are also being considered for other compounds, such as polycyclic aromatic hydrocarbons (PAH).
Another method for cleaning soil contaminated with petroleum by-products is to process the soil with coal and water. Such a process is described in U.S. Pat. No. 5,019,245. The process produces clean soil and coal agglomerates using flotation, wherein the agglomerates will contain the bulk of the oils, tars and other hydrocarbon residues. However, the extraction of oil-contaminated soils by hot water processing and flotation may not always be possible due to either poor flotation response, poor selectivity and/or the generation of froth that is difficult to handle. In addition, the high viscosity of hydrocarbon contaminants, as well as the presence of charred materials with particle sizes over 0.6 mm, can contribute significantly to the poor release of contaminants from the soil.
While the typical approach for treating contaminated soil is to remove the contaminants, the present invention is directed to a method for treating oil and tar contaminated soil that will render the soil non-hazardous by eliminating or reducing the tendency of hazardous hydrocarbons to leach out. The soil can thereafter be disposed of by conventional methods, e.g., burning or burial in a landfill.
An object of the present invention is to provide an inexpensive process for cleaning soil contaminated with oil, tar and other hydrocarbon residues.
Another object of the present invention is to provide a treatment for contaminated soil that will render the soil non-hazardous.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.